This invention relates to engine management systems and more particularly to a fuel management system that uses a single nozzle direct injection system for directly injecting a rapidly variable ratio of an anti-knock agent and gasoline into a cylinder in order to prevent knock as the engine torque is increased. The anti-knock agents that can be used include ethanol and methanol.
On demand use of directly injected (DI) ethanol or other anti-knock agents in spark ignition engines that also employ gasoline direct injection is very attractive as a means to control knock and enable operation of the engine at much higher levels of torque/horsepower. Computer model calculations have shown that relative to port injection of gasoline and direct injection of the anti-knock agent, the direct injection of gasoline as well as the anti-knock agent can significantly reduce the amount of anti-knock agent required over a drive cycle. Typically, multiple sets of injectors would be required for separate injection of gasoline and an anti-knock agent. However, the use of multiple sets of injectors may be prohibited by available cylinder head space, is complex and therefore expensive.
In order to address the drawbacks of multiple injectors, the use of a single nozzle configuration is discussed in U.S. Pat. No. 7,225,787, the contents of which are incorporated herein by reference. This patent does not discuss, however, how to mix the gasoline and anti-knock agent outside of the injector, and in particular, that patent does not disclose means for mixing the gasoline and the anti-knock agent so as to minimize the cost of the system through the use of a single high pressure pump. It also does not discuss means to insure that adequate knock suppression will be provided during transient conditions as the engine torque increases. Because of the finite volume between a proportioning valve and the injector, and the finite rate of fuel consumption, there is a natural delay in adjusting the anti-knock agent to gasoline ratio that is injected into the cylinder. This delay, referred to as a “fuel composition adjustment delay”, can result in knocking conditions when the engine operation changes from low torque to high torque. The reverse situation, when the engine operation changes from high torque to low torque does not result in increased tendency to knock and the fuel composition adjustment delay results only in slightly increased anti-knock agent utilization.
An object of the present invention is a fuel management system for operation of a direct injection spark ignition gasoline engine that eliminates the need for multiple injector sets when direct injection of an anti-knock agent is employed to prevent knock as the engine torque increases.